Such bending inertial vibration transducers are discussed in WO01/54450 and may employ a plate-like piezoelectric member that resonates in bending. A mass may be provided on the piezoelectric member. Coupling means, typically a stub, are provided for mounting the transducer to a site to which force is to be applied from or to the member. The member is free to bend and so generate a force via the inertia associated with accelerating and decelerating its own mass during vibration. The bending of the member can either be in response to an electrical signal, in which case the transducer acts as a vibration exciter, or can generate an electrical signal, in which case the transducer acts as a vibration sensor.
WO03/009219, also incorporated by reference, discloses the use of a greetings or similar card in the form of a folded member having a front leaf and a rear leaf. A bending inertial vibration transducer of the kind disclosed in WO01/54450 is attached to one of the leaves by way of a small stub in order to vibrate the leaf. The leaf is configured as a bending wave member for converting this vibration into acoustic radiation, as discussed e.g. in WO97/09842. The transducer is driven by a signal generator/amplifier/battery unit, which is actuated by a switch concealed in the fold of the card so as to activate the signal generator when the card is opened. As is known, such bending wave members may also act as microphones, converting acoustic radiation into vibration which can then be converted into an electrical signal by a transducer.